Hybrid electric vehicles selectively use an internal combustion engine as a source of input torque to a transmission, alone or in conjunction with one or more traction motor(s), while extended-range electric vehicles use a smaller engine only when needed, and solely to power an electric generator. Battery electric vehicles forego use of the small gas engine, and instead operate using stored electrical energy or regenerative braking energy. All three vehicle configurations can operate solely on electricity in what is referred to as an electric vehicle (EV) mode.
Some electric vehicles utilize a heat pump system to heat and cool the vehicle passenger compartment, utilizing a front-end heat exchanger as the evaporator and an accumulator-type refrigerant system. In such systems the front-end heat exchanger may ice-up over time and require a de-icing function, which causes low-capacity heating in mild and cold ambient temperatures.